Cooling of finely divided solids to prevent afterburning in a regeneration lane



Jan. 10, 1956 N. P. PEET 2,730,508

COOLING OF FINELY DIVIDED SOLIDS'TO PREVENT AFTERBURNING IN AREGENERATION LANE. Filed Nov. 29 1951 T0 GOTTRELL PRECIPITA TOR PR ODUCT DISPERSE PHASE DISPERSE PHASE REGENERATOR REACTOR FIG. I

REGENERATED CA TALYST 22 -FEED AIR 3/ T0 COTTRELL PRECIPI TA TORREGENERATOR 26 12 48 REGENERA TOR DISPERSE PHASE /2 l oer/s5 Prmsz 4 A54 l REGENERATED carausr DENSE muss I3 g; 5. T ,-2 A 23 FIG 3 g: i 2/ 2?.I? s an/r CATALYST q 22 INVENTOR. 4W1

- NICk P. Peer,

FIG. 2-

AGENT- arators. Preferably,

solids in the regeneration gases.

COOLING OF FlNELY DIVIDED SOLIDS T PRE- VENT AFTERBURNING IN AREGENERATION LANE Nick P. Peet, Baytown, Tex., assignor, by mesneassignments, to Esso Research and Engineering Company, Elizabeth, N. .L,a corporation of Delaware Application November 29, 1951, Serial No.253,91'l2 Claims. (Cl. 252-417) The present invention is directed to amethod and apparatus for cooling gases and finely divided solids in agaseous suspension. More particularly, the invention is directed to amethod for preventing afterburning in a suspension of finely dividedsolids in a combustible gas.

The present invention may be briefly described as involving the coolingof a suspension of finely divided solids in a combustible regenerationgas at an elevated temperature in which the gas is caused to flow intoat least two serially connected separation stages to cause separationbetween the finely divided solids and the combustible regenerationgases, the particular feature of the present invention being to cool thegases between the separation stages. By cooling the gases between theseparation stages it is possible to prevent afterburning of thecombustible gases and to allow the obtaining of substantial benefits.

In catalytic cracking and other catalytic operations, it is commonpractice to regenerate the catalyst, which may be finely dividedsilica-alumina, silica-magnesia or silicazirconia. The regeneration iscarried out by suspending the catalyst, which may be contaminated withcarbon and carbonaceous bodies, in a stream of oxygen-containing gaswhich supports a combustion operation in a dense phase in a regenerationzone. By virtue of the combustion operation the carbon and carbonaceousbodies are consumed and a suspension of finely divided catalystparticles is formed in the regeneration gases. The regeneration gasesthemselves are combustible since they com-- prise a substantial quantityof carbon monoxide. The problem of afterburning exists in that, when thesepara- ,tion zones employed in such regeneration operations reduce theamount of catalyst in the suspension, a secondary burning occurs whichis referred to as afterburning. Efforts have been made to reduceafterburning by cooling in the regeneration zone and particularly in thedispersed phase by injecting water into the dispersed phase. Thisoperation has not been completely satisfactory since it results inremoving a considerable amount of heat from the catalyst entrained tothe primary cyclone. Therefore,

"in accordance with the present invention the suspension of catalystinthe separation zones is cooled between stages to prevent suchafterburning and at the same time avoid cooling the major part of thecatalyst entrained to the cyclones. The cooling operation may beconducted in any one of a number of Ways. For example, it is commonpractice to employ cyclone separators in the regeneration vessels nearthe top thereof. The size and capacity of the separators and theregeneration vessels is such that heat transfer means may be interposedbetween the cyclone sephowever, cooling is obtained by injecting betweenstages a cooling fluid at a temperature below the temperature of thesuspension of finely divided For example, cooling may he obtained byinjecting steam at a temperature lower "than the temperature of theregeneration gases or other atent O 2,730,508 Patented Jan. 10, 1956inert gases, such as flue gas or carbon dioxide, nitrogen and the like.Cooling may also be obtained by atomizing water and injecting it betweenstages. It is preferred to employ as a cooling medium steam since watervapor has a high specific heat and will allow the cooling to beperformed efliciently. However, it is within the purview of my inventionto use other inert fluids and even flue gas recovered from the Cottrellprecipitators downstream from the cyclone separators may be used as acooling medium provided the temperature of the flue gas is properlyreduced.

The catalyst employed in operations in accordance with the presentinvention will be of the type mentioned before and will have particlediameters ranging from less than 1 micron up to about 200 microns withthe greater proportion of the catalyst having particle diameters in therange from about 20 to 80 microns. In the cyclone separators the greatmass of catalyst is removed from the regeneration gases and only thecatalyst fines having particle diameters less than 20 microns pass fromthe cyclone separators with the flue gases into Cottrell separators aswill be described further. The larger particles are dropped back intothe dense phase and thence on regeneration flow into the reactor as willbe described further.

The invention will be further described by reference to the drawing inwhich Fig. 1 is a diagrammatic flow sheet showing the flow of catalystbetween the reactor and regenerator and the injection of steam betweenseparation stages in the regenerator;

Fig. 2 is an illustration of the present invention showing the injectionof steam where 3 separation stages are employed; and

Fig. Sillustrates the present invention in which a heat exchanger isinterposed between two separation stages.

Referring now to the drawing in which similar numerals will be employedto identify similar parts and particularly to Fig. l, numeral 11designates a reactor vessel and numeral 12 a regenerator vessel. Line 13conveys regenerated catalyst from vessel 12 into line 14 and thence intoreactor 11. The regenerated catalyst is ad mixed with feed introducedinto line 14 by line 15 from a source not shown. The feed stock may beany one of the numerous feed stocks that are now charged to cata-' lyticcracking units and may be a residual oil or may be a gas oil or anaphtha. For the purpose of this description it is assumed that the feedstock is a gas oil and is admixed with the regenerated catalyst fromline 13 which is at a temperature in the range from 800 to 1200 F. Inreactor vessel 11 which is of suflicient size and capacity the crackingreaction is allowed to take place under conditions of flow such that adense phase of catalyst in the Arranged in the upper portion of thereactor vessel 11 1s a separator or separators, such as Buell cyclone18, which is provided with dip leg 19 for return of catalyst to thedense phase 16. Leading from reactor vessel 11 and separator 18 is line20 which discharges any finely divided catalyst escaping cylone 18 alongwith the cracked product into a fractionation zone for recovery ofdesired cracked products. The fractionation zone is not shown since thedescription thereof is not required for the purposes of this invention.

Spent catalyst from the dense phase 16 is withdrawn by line 21 and isadmixed with air introduced by line 22 and thence introduced by line 23into regeneration 12 wherein a combustion operation takes place in thedense phase indicated generally by 24 in the lower portion thereof.

been described with respect to Above the dense phase in regeneratorvessel 12 is a disperse phase in the upper part of the vessel, the flowconditions being such to maintain the disperse phase above the densephase.

-In the upper part of the vessel 12 in the disperse phase 25 are locatedseparation stages 26 and 27 connected in series by a conduit or .line28. These separators may be illustrated by the Buell cyclone well knownto the art. Separator 26 is provided with a dip leg 29 which returnsseparated catalyst to the dense phase 24 and separator 27 is providedwith a dip leg 30 which returns separated catalyst also to dense phase24.

Separator 27 is connected to an outlet line 31 which dischargesregeneration gases containing catalyst fines to a Cottrell precipitator,not shown. The stream in line 31 is a suspension of catalyst fines influe gas.

The afterburning problem which has been encountered has occurred in theseparation stages and particularly downstream from the separation stage26. Therefore, in accordance with the present invention, a coolingfluid, such as steam, is introduced into line 28 by line 32. This steammay be at a temperature ranging from 250 to 350 F., which issubstantially below the temperature, which may range from 800 to 1200F., in the regeneration vessel 12 by virtue of the combustion operationtherein which the carbon and carbonaceous bodies are removed from thecatalyst.

Referring now to Fig. 2 a regenerator vessel 12 in which a dense phase24 and a dispersed phase 25 is obtained as a result of propermaintenance of flow conditions has arranged therein a plurality ofseparation stages 40, 41, and 42 which are similar to separation stages26 and 27 and may be Buell cyclones. Separation stage is provided with adip leg 43 for returning catalyst to the dense phase 24. Separator 41 isprovided with a dip leg 44 also for returning the catalyst to the densephase 24 while separator 42 is provided with a dip leg 45 also forreturning catalyst to dense phase 24. Separation stage 40 is connectedto separation stage 41 by a conduit 46 and separation stage 41 isconnected to separation stage 42 by a conduit 47. Separation stage 42 isconnected by line 31 to a Cottrell precipitator, not shown, whereincatalyst fines are recovered from the regeneration gases. Connectinginto line 46 is line 48, which allows a cooling fluid, such as steam, tobe introduced between separation stages 40 and 41. A similar line 49allows steam to be introduced into line 47 between separation stages 41and 42.

Referring now to Fig. 3 a regenerator vessel 12, as has Figs. 1 and 2,has arranged therein separation stages 26 and 27. It will be noted thatregenerator 12 is operated under conditions to provide a dense phase 24and a disperse phase 25. Interposed between separation stages 26 and 27is a heat exchanger or cooling means 60 which is connected to separationstage 26 by conduit 61 and to separation stage 27 by a conduit 62.Arranged in heat exchanger 60 is a cooling coil 63. Connected to coolingcoil 63 is line by way of which a cooling fluid is introduced into thecooling means 60. Line 65 is provided to withdraw the cooling fluid fromheat exchanger 60 and allow circulation through the cooling coil 63. Byvirtue of the heat exchanger 60 provided with a cooling coil 63interposed between the separation stages 26 and 27, it is possible tocool the combustible regeneration gases and the solids contained thereinas the suspension passes from separation stage 26 to separation stage27. By virtue of this cooling operation afterburning is eflcctivelyprevented.

The cooling fluid introduced into the heatexchang'er 60 may be the feedstock itself for economy of heat utilization or it may be cooling wateror even a suitable refrigerant, such as liquefied petroleum gases,ammonia and the like. Since the purpose of the cooling fluid is toreducethe temperature of the suspension, including combustible gases andsolids to prevent afterburning downstream from and in the separationstages after reducing the content of solids in the suspension, anysuitable cooling fluid may be used provided the temperature of thecooling fluid is such to reduce the temperature of the combustibleregeneration gases by an amount in the range from 50 to F. depending onthe level at which regeneration is conducted.

Thus, in accordance with the present invention, afterburning of thecombustible regeneration gases is prevented by introducing steam eitherthrough line 32 with respect to Fig. l to prevent afterburningdownstream from the separation stages or through lines 48 and 49 withrespect to Fig. 2 for the same purpose. As pointed out before, the sameeffect can be obtained by direct cooling between stages by providingsuitable heat exchange equipment as shown in Fig. 3.

In order to illustrate the invention further, efiective prevent on ofatterburning was obtained in a catalytic cracking unit in which aregeneration temperature of ll35 F. was employed. This afterburning wasprevented by using 14,500 pounds per hour of cooling steam between theseparation stages. This was suflicient to cool the flue gas to l060 F.In subsequent operations it was established that afterburning didnotoccur in the disperse phase at temperatures as high as 1150 F. providedthe substantially catalyst-free flue gas downstream of the first stagewas cooled to a temperature of 1060 F. The concentration of catalystentrained in the flue gas to the primary cyclones or separation zones atthis unit during the above operations was about 0.2 pound per cubicfoot. The concentration of catalyst at the outlet of the first stage wasapproximately 0.04 pound per cubic foot.

By virtue of cooling between stages it was possible in this commercialoperation to increase the fresh feed rate to the equivalent of reactorvessel 11 by approximately 2400 barrels per day. In addition, theincreased burning rate possible by employment of higher regeneratortemperatures than ordinarily practicable without cooling between stageshas resulted in a reduction in the carbon in the regenerated catalystfrom about 1.0% to 0.6%.

In other operations a regenerator temperature of 1125 F. was employedsuccessfully without afterburning of the regenerator gases. Thetemperature in the flue gas line, equivalent to line 31, has beenmaintained at 1060" F. with no indication of afterburning at regeneratortemperatures up to 1140 F. In these operations the concentration ofcatalyst in the flue gas entering the first cyclone was approximately1.0 pound per cubic foot.

Experience in commercial units has demonstrated that afterburning willnot occur when the present invention is employed at regeneratortemperatures as high as 1150' F. at a catalyst concentration of flue gasof 0.2 pound per cubic feet. It is contemplated that a temperature of1200 F. may be employed without afterburning by virtue of the benefitsallowed in accordance with the present invention.

The nature and objects of the present invention having been completelydescribed and illustrated, what I wish to claim as new and useful and tosecure by Letters Patent is:

1. A method for regenerating finely divided catalytic solids containingcarbon and carbonaceous bodies which comprises suspending said finelydivided solids in a free oxygen-containing gaseous stream, burningcarbon and carbonaceous bodies from said finely divided solids in aregeneration zone at a temperature in the range from 800 to 1200 F. toform a suspension of said solids in a combustible regeneration gas,reducing the solids content of said suspension in a first separationstage in said regeneration zone, flowing said suspension of reducedsolids content into a second separation stage in said regeneration zoneto reduce further the solids content of the suspension, introducing aninert cooling fluid into said suspension of reduced solids contentflowing between said stages to lower the temperature of the suspensionof reduced solids content flowing into the second stage by 50 to 150 F.to prevent afterburning in said suspension of reduced solids contentdownstream from said first stage while maintaining the temperature ofthe catalytic solids in said regeneration Zone in the range between 800and 1200 F., and then discharging a substantially solids-free gas fromsaid second stage and said regeneration zone.

2. A method in accordance with claim 1 in which the cooling fluid issteam.

3. A method in accordance with claim 1 in which the cooling fluid isflue gas.

4. A method in accordance with claim 1 in which the cooling fluid iswater.

5. A method in accordance with claim 1 in which the cooling fluid issteam at a 250 to 350 F.

UNITED STATES PATENTS Belchetz May 1, Thomas et al. Jan. 29, ArvesonApr. 22, Le Roi Nov. 23, Scheineman Nov. 15, Strader Jan. 31, Kuhn Dec.19, Muly et a1. Mar. 13,

Payne J an. 1,

temperature in the range from

1. A METHOD FOR REGENERATING FINELY DIVIDED CATALYTIC SOLIDS CONTAININGCARBON AND CARBONACEOUS BODIES WHICH COMPRISES SUSPENDING SAID FINELYDIVIDED SOLIDS IN A FREE OXYGEN-CONTAINING GASEOUS STREAM, BURNINGCARBON AND CARBONACEOUS BODIES FROM SAID FINELY DIVIDED SOLIDS IN AREGENERATION ZONE AT A TEMPERATURE IN THE RANGE FROM 800* TO 1200* F. TOFORM A SUSPENSION OF SAID SOLIDS IN A COMBUSTIBLE REGENERATION GAS,REDUCING THE SOLIDS CONTENT OF SAID SUSPENSION IN A FIRST SEPARATIONSTAGE IN SAID REGENERATION ZONE, FLOWING SAID SUSPENSION OF REDUCEDSOLIDS CONTENT INTO A SECOND SEPARATION STAGE IN SAID REGENERATION ZONETO REDUCE FURTHER THE SOLIDS CONTENT OF THE SUSPENSION, INTRODUCING ANINERT COOLING FLUID INOT SAID SUSPENSION OF REDUCED SOLIDS CONTENTFLOWING BETWEEN SAID STAGES TO LOWER THE TEMPERATURE OF THE SUSPENSIONOF REDUCED SOLIDS CONTENT FLOWING INTO THE SECOND STAGE BY 50* TO 150*F. TO PREVENT AFTERBURNING IN SAID SUSPENSION OF REDUCED SOLIDS CONTENTDOWNSTREAM FROM SAID FIRST STAGE WHILE MAINTAINING THE TEMPERATURE OFTHE CATALYTIC SOLIDS IN SAID REGENERATION ZONE IN THE RANGE BETWEEN 800*AND 1200* F., AND THEN DISCHARGING A SUBSTANTIALLY SOLIDS-FREE GAS FROMSAID SECOND STAGE AND SAID REGENERATION ZONE.